2r^2-r-7=0

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Solution for 2r^2-r-7=0 equation:


Simplifying
2r2 + -1r + -7 = 0

Reorder the terms:
-7 + -1r + 2r2 = 0

Solving
-7 + -1r + 2r2 = 0

Solving for variable 'r'.

Begin completing the square.  Divide all terms by
2 the coefficient of the squared term: 

Divide each side by '2'.
-3.5 + -0.5r + r2 = 0

Move the constant term to the right:

Add '3.5' to each side of the equation.
-3.5 + -0.5r + 3.5 + r2 = 0 + 3.5

Reorder the terms:
-3.5 + 3.5 + -0.5r + r2 = 0 + 3.5

Combine like terms: -3.5 + 3.5 = 0.0
0.0 + -0.5r + r2 = 0 + 3.5
-0.5r + r2 = 0 + 3.5

Combine like terms: 0 + 3.5 = 3.5
-0.5r + r2 = 3.5

The r term is -0.5r.  Take half its coefficient (-0.25).
Square it (0.0625) and add it to both sides.

Add '0.0625' to each side of the equation.
-0.5r + 0.0625 + r2 = 3.5 + 0.0625

Reorder the terms:
0.0625 + -0.5r + r2 = 3.5 + 0.0625

Combine like terms: 3.5 + 0.0625 = 3.5625
0.0625 + -0.5r + r2 = 3.5625

Factor a perfect square on the left side:
(r + -0.25)(r + -0.25) = 3.5625

Calculate the square root of the right side: 1.887458609

Break this problem into two subproblems by setting 
(r + -0.25) equal to 1.887458609 and -1.887458609.

Subproblem 1

r + -0.25 = 1.887458609 Simplifying r + -0.25 = 1.887458609 Reorder the terms: -0.25 + r = 1.887458609 Solving -0.25 + r = 1.887458609 Solving for variable 'r'. Move all terms containing r to the left, all other terms to the right. Add '0.25' to each side of the equation. -0.25 + 0.25 + r = 1.887458609 + 0.25 Combine like terms: -0.25 + 0.25 = 0.00 0.00 + r = 1.887458609 + 0.25 r = 1.887458609 + 0.25 Combine like terms: 1.887458609 + 0.25 = 2.137458609 r = 2.137458609 Simplifying r = 2.137458609

Subproblem 2

r + -0.25 = -1.887458609 Simplifying r + -0.25 = -1.887458609 Reorder the terms: -0.25 + r = -1.887458609 Solving -0.25 + r = -1.887458609 Solving for variable 'r'. Move all terms containing r to the left, all other terms to the right. Add '0.25' to each side of the equation. -0.25 + 0.25 + r = -1.887458609 + 0.25 Combine like terms: -0.25 + 0.25 = 0.00 0.00 + r = -1.887458609 + 0.25 r = -1.887458609 + 0.25 Combine like terms: -1.887458609 + 0.25 = -1.637458609 r = -1.637458609 Simplifying r = -1.637458609

Solution

The solution to the problem is based on the solutions from the subproblems. r = {2.137458609, -1.637458609}

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